The present invention relates to a control system for a hydraulic circuit for operating a plurality of actuators simultaneously.
As shown in FIG. 39, a hydraulic excavator, which is a construction machine, has an undercarriage 51 and an upper structure 53, which is mounted on the undercarriage 51 and adapted to be rotated by a turning actuator 52. The base end of a boom 55, which is adapted to be swung by boom actuators 54, is secured to the upper structure 53 by a shaft. The base end of a stick 57, which is adapted to be swung by a stick actuator 56, is secured to the fore end of the boom 55 by a shaft. An attachment 59 or a bucket, either of which is adapted to be pivoted by a bucket actuator 58, is secured to the fore end of the stick 57 by a shaft. The attachment 59 is a working tool to be operated by an attachment actuator 60.
Such a hydraulic excavator as described above is provided with two pumps so that hydraulic pressures and flow rates are supplied to the actuators 52,54,56,58,60 through parallel passages by control valves that are connected to the two pumps.
Some of these actuators 52,54,56,58,60 operate by confluent flows of hydraulic oil from the two pumps, while there are those that operate solely by hydraulic oil supplied from either pump.
In the case of a hydraulic excavator, the boom actuators 54, the stick actuator 56, and the attachment actuator 60 operate by confluent flows of hydraulic oil from the two pumps. Examples of the actuators that operate solely by hydraulic oil supplied from either pump include the turning actuator 52 and the bucket actuator 58.
The attachment actuator 60, which requires a high flow rate exceeding the delivery rate of a single pump, must be driven by joining the flows of hydraulic oil from both pumps.
When operating the attachment actuator 60, which has a feature described above, simultaneously with an actuator of a 2-pump confluent type, such as the boom actuators 54 or the stick actuator 56, there arises a problem characteristic to parallel connection of actuators; the hydraulic oil tends to concentrate in the actuator with the lowest working pressure, thereby drastically slowing operation of the other actuators.
For example, when using an open/close breaker or the like as the attachment 59, the working pressure for the attachment actuator 60 to open or close the breaker is lower than the working pressure for the boom actuators 54 or the stick actuator 56 to raise the boom 55 or the stick 57. Therefore, when an operating device is operated to raise the boom 55 and/or the stick 57 while opening or closing the attachment 59, neither the boom actuators 54 nor the stick actuator 56 is actuated until the attachment actuator 60 with the lower working pressure reaches the end of its stroke. It is thus difficult to operate these actuators in optimal synchronization.
In order to solve the above problem, an object of the present invention is to improve the function of the machine when operating a specific actuator which requires a high flow rate simultaneously with other actuators.
A hydraulic circuit control system according to the invention includes one or more specific control valves for controlling hydraulic fluid supplied from one or more pumps to a specific actuator, one or more other control valves for controlling hydraulic fluid supplied from said pump(s) to one or more other actuators, discriminating means for distinguishing between control conditions for operating said specific actuator alone and control conditions for operating the same simultaneously with any of the other actuators, and a controller for controlling control characteristics of the specific control valve(s) based on discriminated control conditions.
With the configuration as above, the discriminating means is capable of distinguishing the mode of operating the specific actuator by hydraulic fluid supplied from the pump(s) between operating it alone and operating it simultaneously with any of the other actuators. Therefore, when the specific actuator is operated in the combined operation mode, the specific control valve(s) and the other control valve(s) are controlled to effect optimal balance between these valves so that combined operatability of the specific actuator and the other actuator(s) is improved. When the specific actuator is operated alone, a high flow rate required by the specific actuator is ensured.
A hydraulic circuit control system according to another feature of the invention is characterized in that said one or more pumps are comprised of a plurality of pumps; said one or more specific control valves are comprised of a plurality of control valves respectively corresponding to said plurality of pumps; said one or more other control valves are comprised of a plurality of control valves respectively corresponding to said plurality of pumps; and that the controller has functions of storing control characteristics for each respective control valve and choosing the characteristics most suitable for the control conditions from among a plurality of control characteristics stored therein.
Therefore, upon receiving control conditions from the discriminating means, the controller is capable of controlling the specific control valves, which are respectively associated with the plural number of pumps, with the characteristics that have been selected from a plurality of control characteristics stored beforehand so as to be most suitable for the control conditions. As a result, the actuator is ensured of superior operatability in the combined operation mode and a high flow rate in the single operation mode.
A hydraulic circuit control system according to yet another feature of the invention is characterized in that two each pumps and specific control valves are provided and that the controller has such a function that when ascertaining combined operation of the specific actuator with any of the other actuators, the controller automatically adjusts control signals to be output to the two specific control valves so as to switch the source of hydraulic fluid to the specific actuator from the two pumps to either one of the two pumps according to pump-selecting criteria for the combined operation mode, which criteria have been set beforehand with respect to the other actuators.
With the configuration as above, when the specific actuator is operated together with any of the other actuators, one of the lines of the hydraulic fluid discharged from the two pumps is closed off by one of the two specific control valves, and the hydraulic fluid in the closed line is fed through the other control valves to the other actuators. Therefore, even when the specific actuator is operated at a pressure lower than that applied to the other actuators, combined operatability of the specific actuator and the other actuators can be improved.
A hydraulic circuit control system according to yet another feature of the invention is characterized in that the controller has a function of storing a plurality of control patterns consisting of a plurality of grouped control characteristics of the specific control valves and that the hydraulic circuit control system includes a control pattern selecting device for selecting from these control patterns the pattern most appropriate for the specific actuator.
When the specific actuator is replaced by an actuator of another kind, the control pattern selecting device permits the collective setting of a plurality of control characteristics by merely selecting the appropriate pattern for the kind of the specific actuator to be used. By thus eliminating the complication of re-setting control characteristics for each attachment individually, adjusting operation that is necessary when changing the specific actuators is facilitated.
The controller of a hydraulic circuit control system according to yet another feature of the invention is provided with a control pattern that includes such control characteristics as to reduce the output signal ratio with respect to the amount of operation to be input into the specific control valves when the controller ascertains combined operation and a great load being applied to the other actuators. Therefore, by reducing the output signal ratio with respect to the amount of operation to be input into the specific control valves so as to increase by the reduced amount the pressure of the hydraulic fluid applied to the other actuators that are exposed to a heavy load, combined operation of the specific actuator and the other actuators can be optimized.
The controller of a hydraulic circuit control system according to yet another feature of the invention is provided with a control characteristic overwriting device adapted to overwrite control characteristics currently stored in the controller with other control characteristics that correspond to some other actuator. Therefore, when using some other specific actuator that was not originally to be used, the control characteristic overwriting device permits the control of the hydraulic circuit with the optimal control characteristics by overwriting the control characteristics at any desired time.
According to yet another feature of the invention, the specific actuator is an attachment actuator for operating the attachment attached to the fore end of the working device of a hydraulic excavator, and the other actuators are working actuators other than the attachment actuator. Therefore, the invention is capable of improving combined operatability of the attachment actuator and the other actuators, said attachment actuator being the actuator that requires the highest flow rate among all the actuators of the working device of a hydraulic excavator. The invention also ensures the attachment actuator to be operated at the maximum speed when it is operated in the single operation mode.
The controller of a hydraulic circuit control system according to yet another feature of the invention is capable of storing a plurality of control patterns consisting of a plurality of control characteristics of the specific control valves, which characteristics are grouped in accordance with a plurality of attachments that can be interchangeably attached to the same working device, and the controller is provided with a control pattern selecting device for choosing, when the attachment is changed, a pattern appropriate for the actuator of the newly connected attachment from among these control patterns.
This feature is particularly effective in demolition or other work that must be performed while changing a plurality of attachments, because there is no need of setting or adjusting control conditions each time the attachment is changed; rather than setting or adjusting control conditions each time the attachment is changed, a plurality of control characteristics can be set collectively by choosing the control patters appropriate for the attachments to be used from among a plurality of control patterns that have been formed beforehand by grouping a plurality of control conditions. Therefore, the invention is effective in facilitating adjusting operation when changing the attachment.